The present invention relates generally to the field of communication networks and in particular to a system and method for handing off a call between circuit switched and packet data wireless networks.
The emerging technology for core networks in wireless communication systems is a packet-based, all-IP network. For example, the IP Multimedia System (IMS) is a open industry standard architecture for telecom operators to provide voice and multimedia communication services. The IMS network runs over the standard Internet Protocol (IP), providing both Voice over IP (VoIP) and data services, including audio and video broadcast or streaming, videoconferencing, games, filesharing, e-mail, and the like. The IMS network supports both packet data wireless networks, such as CDMA 1x EV-DO, WLAN (WiFi), WiMAX, WCDMA, HSPDA, and the like, as well as circuit switched wireless networks, such as CDMA 1x, GSM, and WCDMA.
While the migration toward packet data networks is expected to continue, circuit switched wireless communication networks are widely deployed and heavily used. A heterogeneous mix of a circuit switched and packet data wireless networks will exist in the field for years to come.
Mobility management is a key aspect of wireless communication systems, necessary to maintain communications with mobile terminals as users move throughout different geographic areas. Mobile Assisted Hand-Off (MAHO) is a well-known element of mobility management. In MAHO, mobile terminals report channel conditions, desired data rates, pilot strengths signals from neighboring radio base stations, and the like to a serving base station, which, using this information as well as the relative loading among neighboring base stations, determines if, when, and to which base station to hand off a mobile terminal. Intra-system handoff is a fundamental operational aspect of any wireless communication system.
Inter-system handoff, however, may be problematic for several reasons. First, mobile terminals must be developed and deployed to that are capable of engaging in communications with both circuit switched and packet data wireless networks. Additionally, in most deployments, circuit switched and packet data wireless networks operate in different frequency bands. Hybrid mobile terminals exist which can operate in both frequency bands simultaneously; however soft inter-system handoff is impossible due to the different radio technologies used. Additionally, network protocols in the circuit switched and packet data systems do not directly support inter-system handoff.